A power transistor used in the switched mode, as in an inverter or converter, should be driven to saturation (or quasi-saturation) to minimize the voltage drop across the transistor. The base drive current required is a function of the transistor collector current.
A commonly used circuit provides base current sufficient to achieve saturation for peak transistor current. This approach has the advantage of simplicity but is inefficient when the transistor handles less than peak current.
Proportional base drive circuits are known in which base current is continuously adjusted as a function of the collector current. Such circuits are complex and expensive.